Just a reminder that UK Border Force can confiscate all of your electronic devices for 7 days and you have to give them all your passwords to these devices and associated accounts - refusing to do so is punishable by up to 2 years in prison. And no, they don't need any warrant, just a probable cause. If you want to see more how that looks like this is a video by a guy who experienced it first hand:
https://www.youtube.com/watch?v=991kRp8KUmo&t=1s
